Cold Waves in Northwest India

In Context

• The India Meteorological Department has predicted a cold wave in parts of Northwest India.

What is Cold Wave?

• The IMD defines a cold wave qualitatively as “a condition of air temperature which becomes fatal to the human body when exposed.”
• According to the IMD, cold wave conditions occur when the mercury falls below 10 degrees Celsius in the plains, and the minimum temperature stays at least 4.5 degrees to 6.4 degrees Celsius below the normal level. 
• Conditions favourable for cold wave are:
  • Inflow of cold air mass from higher latitudes over the region in the rear of the passage of a well marked low pressure system in the westerly wind flow of mid-latitudes.
  • Foggy weather during the day which inhibits day warming of the region.
  • Strong radiation cooling during th3 night under clear sky conditions.

Cold wave over India 

• Cold waves over the country are generally experienced during December -February. 
• The frequency of occurrence of cold waves is over northwestern parts of India.
• Occurrence of cold waves is associated with the inflow of very cold air from extreme  northwestern parts of the Indian-subcontinent or even beyond. 

Reasons Behind Cold Waves Formation

• Snowfall: In the upper Himalayas are responsible for the wind chill factors
• Western Disturbances: Due to the lack of western disturbances which are extratropical storms that mostly appear during the winter months. The cold winds from the Himalayas continue to blow into the northern parts of India thereby allowing the prevailing cold conditions to continue and intensify. 
  • Western disturbances are storms that originate in the Mediterranean region and bring winter rainfall to northwest India.
• La-Nina Effect in the Pacific. La Nina is the abnormal cooler sea surface temperatures reported along the equatorial Pacific Ocean and it is known to favour cold waves.
• Absence of cloud cover: Clouds trap some of the outgoing infrared radiation and radiate it back downward, warming the ground.
• North Atlantic Oscillation (NAO) and the Siberian High.

Impacts 

• Impact Agriculture: It can destroy the Rabi crop and affect the productivity of cash crops (Coffee, Tea). There would be a wider gap between day and night temperature.
• Impact on Health: The cold wave is extremely fatal to human health, it could affect vulnerable people (infants, pregnant women, elderly, people) with chronic diseases.
  • Likelihood of illnesses like flu, due to prolonged exposure to the cold.
• Impact visibility: The cold wave can affect the visibility and which can be more prone to accidents, loss of life due to accidents.

Source: IE